Peroxidation of lipids in cell membranes has been proposed as a mechanism of toxicity caused by xenobiotic chemicals (e.g., geminal substituted halogenated alkyl compounds), by ischemic tissue injury (e.g., reperfusion injury), and by altered biochemical processes that occur in aging as well as several disease states such as atherosclerosis and cancer. The long-term objectives of this proposal are to identify accessible biomarkers of in vivo lipid peroxidation, and to develop sensitive yet practical assays for these biomarkers as dosimeters of exposure in vivo to agents and/or conditions that cause lipid peroxidation. Inasmuch as reactive aldehydes are significant products of lipid peroxidation that can bind to tissue macromolecules, the specific aims of this proposal are: 1) to develop a sensitive assay (gas chromatography with nitrogen-phosphorus detection) for hydrazine derivatives of two major aldehydes of lipid peroxidation, malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), 2) to synthesize, characterize, and develop assays (HPLC with fluorometric detection) for amino acid adducts of MDA and 4-HNE both as possible urinary marker metabolites of lipid peroxidation and as possible markers of MDA and/or 4-HNE bound to proteins, such as hemoglobin, an accessible protein that has a relatively long half-life in vivo, and 3) to use the assays developed to determine the concentration of these lipid peroxidation products over time in rats and mice after the administration of hepatotoxic doses of halogenated alkanes, and after other treatments and conditions that are known to cause lipid peroxidation.